Vent for tapered bore gun



April 24, 1956 L. R. SWEETMAN VENT FOR TAPERED BORE GUN Filed April 17,1945 Fig]- L ER DY H-5WEET MAN VENT FOR TAPERED BORE GUN Leroy R.Sweetman, Washington, D. C., assignor to the United States of America asrepresented by the Secretary of War Application April 17, 1945, SerialNo. 588,878

2 Claims. (Cl. 89-14) (Granted under Title 35, U. S. Code (E52), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment to meof any royalty thereon.

This invention relates to improvements in tapered bore guns and moreparticularly to venting means for eliminating the mutilation of the casewhich invaribly occurs in firing a conventional tapered bore gun.

Tapered bore guns of large caliber have proven very eifective inanti-tank and armor piercing uses, especially in 57 mm.40 mm. size. Theadvantages of employing a tapered bore together with a deformableprojectile are that a projectile of the smaller cross section isobtained, thus having a reduced wind resistance resulting in betterstability in range, enabling more favorable types and amounts of powder,relative to the projectile weight to be used, producing greater muzzlevelocity; and the life of the barrel is prolonged over that of a barrelof the smaller diameter employing powder in the proportion used in abarrel of the larger diameter. However, the advantage of the taperedbore has been partially lost by the disadvantage of the shell beingmutilated, due to the fact that the mutilated shell scores the breechand pre vents re-sizing and re-use of the case as is customary in theArmy.

This mutilation of the case is caused by the formation of a pressurewave in the bore created when the deformable projectile enters thetapered section, producing momentary decrease in velocity thereof. Sincethe gas pressure is extremely high, approximately 50,000 pounds persquare inch, the action of the gas is analogous to the action of liquidsunder pressure. Since the pressure front is moving toward the muzzle,this momentary deceleration creates a back pressure wave toward thebreech which mutilates the case end.

It is, therefore, a primary aim of this invention to provide means forventing the bore of the barrel to neutralize this back pressure wave andto permit it to escape into the atmosphere.

More particularly, it is an object of this invention to provide ventsdisposed in the forward end of the enlarged portion of the barrel oradjacent the rear end of the tapered section to eliminate the backpressure wave.

Still a further aim of the invention is to provide vents so arrangedthat they will not only function to eliminate the back pressure wave,but will also function as a muz zle brake to reduce the recoil and, inaddition, to compensate for the recoil vertical jump of the gun.

Still another object of the invention is to form the bore with arecessed section into which the vents open so that the projectile skirtswill not close the vent openings at the instant that the back pressurewave is created and so that the skirts will not extrude into the ventopenings and thereby cause erosion of the bore around the vents.

Other objects and advantages of the invention will hereinafter becomemore fully apparent from the following description of the drawing, whichillustrates preferred embodiments thereof, and wherein:

2,742,821 Patented Apr. 24, 1956 "ice Figure 1 is a longitudinal,substantially central sectional view of a portion of a tapered gunbarrel constructed in accordance with the preferred form of theinvention;

Figure 2 is a cross sectional view of the barrel taken substantiallyalong a plane as indicated by the line 2-2 of Fig. 1;

Figure 3 is a fragmentary, longitudinal substantially central sectionalview of a slightly modified form of the invention;

Figure 4 is a view similar to Fig. 3 of another modification thereof;and

Figure 5 is a view similar to Fig. l and showing another embodiment ofthe invention.

Referring more particularly to the drawing, wherein like referencecharacters designate like or corresponding parts throughout thedifferent views, in Figs. 1 and 2 6 designates generally a portion of agun barrel having a bore including the bore sections 7 and 8. Boresection 7 is of the same diameter throughout its length, whereas boresection 8 is tapered and diminishes from a diameter equal to that ofbore section 7 to a diameter of a smaller caliber bore section, notshown in Figs. 1 and 2, but illustrated in Figs. 3 and 4. In thispreferred embodiment of Figs. 1 and 2, the bore section 8, at the endthereof which joins with bore section 7, is recessed at 9 to provide aportion of greater diameter than either of the sections 7 or 8. Theupper part of the barrel 6 is provided with a plurality of openings orpassages 10 which open into the recessed portion 9 at their inner endsand which open outwardly of the barrel 6 at their outer ends. As seen inFig. 1, the vent openings or passages 10 are inclined to the rear fromtheir inner to their outer ends, for a purpose which will hereinafterbecome apparent. The number and size of the vents 10 will vary dependingupon calibers of the barrel, arrived at as a result of test. In themodified form disclosed in Fig. 3, the barrel 11 includes a largecaliber bore section 12, a smaller caliber bore section 13 and a taperedbore section 14 therebetween, the rear end of which is of the samecaliber as the bore section 12 and the forward end of which is of thesame caliber as the bore section 13. Barrel 11 is provided with ventopenings or passages 15 formed in the forward end of its bore section 12and which open into said section. Vent openings 15 extend entirelyaround the barrel 11 and are likewise inclined rearwardly from theirinner to their outer ends, and may be of any desired number and size asrequired.

The embodiment of the invention shown in Fig. 4 varies only from thatshown in Fig. 3 in that vent openings or passages 16 are formed in therear portion of the tapered, intermediate bore section 17 instead of inthe rear bore section 18.

Another embodiment of the invention is disclosed in Fig. 5, and issimilar to the preferred form as shown in Figs. 1 and 2, in that thetapered bore section 19 is provided with a recessed portion 20, adjacentits rear end, similar to and for the same purpose as the recessedportion 9. In this form of the invention, the vent openings or passages21 may be formed entirely around the barrel and open into the recessedportion 20 and are inclined outwardly and rearwardly. Also, in thisembodiment of the invention, the barrel 22 is formed of sections and thetapered section 19 thereof, at its enlarged end, is provided with anenlarged internally threaded socket 23 for engaging an externallythreaded restricted extension 24 of the enlarged straight barrel section25, for detachably connecting the barrel sections.

From the foregoing, it will be apparent that when a projectile, notshown, of a caliber corresponding to the caliber of the larger boresection of the barrel is fired through any one of the barrels as shownin Figs. 1, 3, 4, and 5, will, 'when it passes from the larger boresection, adjacent the breech end of the barrel, and into the taperedsection where it is deformed, create a back pressure wave which will bereleased through the vents located either at. the rear end of thetapered section or at the forward end of the rear, straight section.This will prevent the back pressure wave from moving back to the breechof the barrel, not shown, and mutilating the open end of the empty shellcase, not shown. While the vent means will function acceptably whenlocated in any of the'positions as shown in the drawing, the preferredposition is as shown in Figs. '1 and 2 wherein the vent passages arelocated near the rear .end of the tapered bore section. By providing therecessed portion 9 or 20,. the skirts of the projectile, not shown, willnot extrude into the vent openings to cause erosion of the 'boretherearound and will not impede the release of the excess pressure. Bygrouping the vent passages in the upper portion of the barrel, as shownin Figs. 1 and 2, the vented pressure is additionally utilized tofunction as a muzzle brake and also to reduce the recoil vertical jump.The grouping of the vents in the upper part of the barrel also preventsan excess amount of flash toward the ground that would reflect againstand expose the gun crew.

It is important to note that the provision of vents to atmosphere in thelocations illustrated do not afiect the exterior ballistics of theprojectile, firstly because gas pressure in the barrel has alreadyreached .a maximum before the vents are reached, and has started todiminish at the time the projectile passes the vents, and secondlybecause of the fact that muzzle velocity of a projectile is dependent toa very large degree upon the ratio of the weight of the projectile tothe type and amount of propellent powder. Firing tests on vented gunbarrels, in which the muzzle velocity was measured, indicated that thevalues obtained were the values .to be expected for the weight ofprojectiles and type and amount .of propellent powder used.

Various additional modifications and changes are contemplated and mayobviously be resorted to, provided that they do not depart from thespirit and scope of the invention as hereinafter defined by the appendedclaims, as only preferred embodiments have been disclosed.

I claim:

1. In a gun barrel having a breech end bore portion of one caliber, amuzzle end bore portion of a lesser caliber, and an intermediate taperedbore portion connecting and merging withthe bores of said end portionsto provide a smooth bore surface, there being a cylindrical recessformed in said intermediate portion of the wall of said barrel andadjacent the connection with said breech end bore portion, said recessbeing of greater diameter than the bore of said breech end portion,there also being a plurality of vents opening outwardly and rearwardlythrough the top portion of the wall of said cylindrical recess.

2. In a gun barrel having a breech end portion of one caliber, a muzzleend portion of a lesser caliber, and an intermediate portion connectingthe bores of said end portions and having a bore tapered from its breechend to its muzzle end, there being a cylindrical recess in the wall ofsaid barrel between said breech part and said intermediate part .ofgreater diameter than the bore of said breech portion, said cylindricalrecess having a plurality of vents extending through its Wall thereofJReferences Cited in the file of this patent UNITED STATES PATENTS 85,949McKenzie Jan. 1-9, 1869 329,303 Fosbery Oct. 27, 1885 592,437 OberhammerOct. 26, 1897 785,975 McClean Mar. 28, 1905 786,230 McClean Mar. 28,1905 1,082,916 Squire Dec. 30, 1913 1,380,171 Abbot May 31, 19211,773,260 Cutts Aug. 19, 1-930 1,944,883 Gerlich Ian. 30, 1934 2,322,370Lance June 22, 1943 FOREIGN PATENTS 437,027 Great Britain Oct. 23, 1 935

